1. Field of the Invention
The present invention relates to a pneumatic spring hammer mechanism or pneumatic percussive tool for a percussive hammer or drill hammer, according to the preamble of patent claim 1.
2. Description of the Related Art
Pneumatic spring hammer mechanisms have long been known in various specific embodiments in which a drive piston is moved back and forth by a crankshaft. In front of the drive piston there is situated a percussion piston that can likewise be moved back and forth, so that between the drive piston and the percussion piston there is formed a hollow space that accommodates an air spring. This air spring, which acts as an air cushion, transmits the movement of the driven drive piston to the percussion piston, which thus follows the movement of the drive piston with a chronological delay. Finally, the percussion piston impacts a shaft of a tool, or of an intermediately connected die, and transfers its impact energy to the tool.
Pneumatic spring hammer mechanisms of this sort have proven effective in practice, both in hammers having electromotor drives and in hammers that operate using an internal-combustion engine.
In particular, the internal-combustion-engine-operated hammers have a centrifugal force coupling between a motor shaft and the crankshaft that decouples the hammer mechanism drive when the internal-combustion engine is rotating at idling speed. In this way, on the one hand an unproblematic idling operation of the engine is ensured, and on the other hand an easier starting of the engine is enabled. Such a centrifugal force coupling is technically costly, requires constructive space, and finally results in a relatively expensive, heavy hammer that is subject to wear.